Optical glass fibers for communication are made from glass such as quartz glass or doped silica glass and are extremely small in diameter and hence weak in strength. Under normal conditions of use, such fibers may be subjected to considerable bending strain and other tensile forces during the cable manufacturing process and while being pulled through ducts and otherwise bent, twisted, or manipulated during reeling or during installation. In the transmission of light signals through optical fiber cables, the signals are readily attenuated in response to relatively small distortions in the cable, such as those caused by the above stresses, sharp bends or roughness in the surface of the fiber to produce light signal distortions or attenuation at an unacceptable level.
To confine the optical signals inside the signal-transmitting fiber core, a glass or silica fiber core is coated with a glass cladding or an amorphous fluoropolymer coating always of a lower refractive index from that of the optical fiber. The coating on the glass cladding may optionally be a silicone, acrylic, polyimide, or other release agent and a polymer coating, which is usually a hard or soft polymer coating which is coated on the fiber from a melt or a solution of the polymer, or extruded onto the fiber.
These considerations also apply to flat ribbon cables embodying a multiplicity of optical fibers arranged parallel to each other. Problems associated with ribbon cables occur in aligning the optical fibers parallel to each other at known and fixed distances apart. It is also crucial for a ribbon cable that is designed to mate with a mass termination system to have exact spacing with respect to a reference point. Crush resistance, flex life, and temperature and flame resistance of the cable can also be problems to be overcome.
Coating and buffering of optical fibers for various purposes are described in U.S. Pat. Nos. 5,002,359, 4,113,350, 4,105,284, 4,380,367, 4,072,400, 3,930,103, 4,463,329, 4,099,837, and 4,642,265 and in a paper in the Bell System Technical Journal, in Volume 54, No. 2, pages 245-262, February 1975, by D. Gloge.